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June l1, 1963
W. P. SCHNEIDER
3,093,811
WELL LOGGING SYSTEMS
6 Sheets-Sheet 1
Filed Nov. 29. 1961
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WELL LoGGING SYSTEMS
Filed NOV. 29, 1961
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WELL LOGGING SYSTEMS
Filed NOV. 29, 1961
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3,093,811
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WELL LOGGING SYSTEMS
Filed Nov. 29, 1961
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signals may be either transmitted via the cable to surface
întlgâßlît
located time measuring means or supplied to time measur
WELL LÜ‘GGENG SYSTEMS
William P. Schneider, Houston, Tex., assigner to Schlum
berger Well Surveying Corporation, Houston, Tex., a
corporation of Terras
Filed Nov. 29, i951, Ser. No. ï55,675
'ì' Claims. (Qi. 34th-i3)
This invention relates to well logging systems and, more
particularly, to acoustic well logging systems for obtaining
measurements of acoustic parameters of a well bore
through which the tool may be passed.
In the acoustic'logging of well bores, considerable ef
forts have been devoted to the measurement of the time
required for an acoustic impulse to travel over a short
vertical section of a well bore and successive time meas
urements for such short sections are recorded as a func
tion of depth.
The derived time measurements are re
ing means in the borehole instrument.
In the latter in
stance, a signal representing a time measurement is con
veyed to surface located indicating means via the cable.
Where the time measuring means are in the borehole
instrument, a time measurement derived by such means is
generally represented by a voltage signal. The downhole
time measurement system is generally complex and ex
pensive due to the instrumentation necessary to withstand
the borehole temperature and pressure conditions, space
limitations, shock, etc., and yet provide a reliable time
measurement signalV under the varying well bore condi-V '
tions. However, this system can provide an analog signal
representing a relatively short time measurement of 40
microseconds to 200 microseconds for a one foot span
between receivers in a T-R-R system. An analog signal
is transmitted through the Cable to surface recording in
struments.
lated to the characteristic velocity of the media forming
To pass the detected signals as sensed by the receivers
the well bore, as well as the porosity of the media. Ob 20
in the borehole instrument directly to the earth’s surface
viously, the accuracy of the time measurements is of eX
has heretofore been undesirable because of the short time
treme importance in providing accurately interpretable
duration between detected signals and the fact that the
results.
cable affects the character of the detected signal. Distor
When one considers that the time measurements are
obtained from a borehole instrument disposed in a well 25 tions of the signal introduce errors in the time measure
ments at the earth’s surface.
bore which may have temperature conditions of up to
The faithful transmission of signals as detected in a
375° F. or more and pressures of 20,000 p.s.i. or more
borehole instrument to the surface instruments via a well
and that electrical signals from the borehole instrument
logging cable with fidelity, however, has now been made
must be transmitted to the earth’s surface over a multi
conductor cable which not only must provide a faithful 30 possible by the use of an armored seven conductor cable
in which six conductors are spirally embedded about a
ransmission path but also supports the weight of the bore
central, seventh conductor with equalizing means being
hole instrument and is also subjected to well bore tem
peratures and pressures, the problems encountered in de
riving an accurate time measurement are seen to be ex
tremely complex. These problems may be neatly classi
ñed in three groups, ie., the borehole instrument, the
transmission and structural characteristics of the cable
and the surface instrumentation.
lt is necessary that the time measurements be reliable
provided for signal transmission purposes. The seventh
conductor has been found ideally suited for the transmis
sion of a signal with fidelity.
Such a cable is described
in a co-pending application assigned to the assignee of the
present invention and is identified as patent application
Serial NO. 79,390, tiled December 29, 1960.
The beneficial transmission characteristics are ascribed
representations of the time required for acoustic energy to 40 mainly to the uniform spacing of the armor wires about
the central conductor where the armor wires provide a1
travel through the media forming the well bore to the
electrical ground. By analogy, therefore, a coaxial type
exclusion of the time required for the acoustic energy to
of cable would also be suitable for the transmission of a
travel between the instrument and the media. Thus, in a
signal with fidelity.
borehole instrument where a single transmitter and re
Nonetheless, even though signals from the borehole
ceiver are used (hereinafter sometimes referred to as a 45
instrument can now be transmitted via the cable to the
T-R system), it is necessary to correct a time measurement
value by an increment of time representing time of travel
of acoustic energy between the instrument and adjacent
media. Since this increment of time is sometimes subject
to error due to irregular spacing of the instrument from
the media, a single transmitter and two receiver system
(hereinafter sometimes referred to as a T-R-R system) has
been developed. In a T-R-R system, the time of arrival
of an acoustic impulse at successive receivers is detected
and the time interval between such detections measured.
Thus, increment of time corrections for acoustic energy
travelling between the instrument and the well bore are
eliminated. However, even in this latter system, errors in
time measurement arise where the instrument tilts relative
to the axis of the well bore or the well bore surface is 60
irregular due to changes in the diameter of the ' ell bore.
Thus, a borehole instrument with a T-l?. or T-R-R system
inherently can be the cause of inaccuracy in time meas
urements because of positioning relative to the wall of the
well bore. Or, in other words, the accuracy of these sys
earth’s surface with fidelity, accurate time measurements
of the travel of acoustic energy along the media forming
the well bore .are dependent upon the relative position of
the borehole instrument in the well bore and accuracy of
time measurement in the time measuring means.
Accordingly, it is an object of the present invention to
provide new and improved acoustic logging systems in
which the accuracy of time measurements at the earth’s
surface is markedly improved.
Another object of the present invention is to provide
new and improved acoustic logging systems in which de
tection of acoustic signals is more accurately determined
in the borehole independent of «the geometry of the well
bore relative to the borehole instrument.
Another object of the present invention is to provide
new and improved acoustic logging systems with overall
increased accuracy in measuring intervals of time.
rThe acoustic logging system in accordance with the
present invention includes a borehole instrument com
prised of an upper transmitter, an upper receiver, a lower
tems depends largely upon a uniform spacing of the
receiver and a lower transmitter which are operated to
transmitters and receiver from the wall of the well bore.
obtain independent signals representing acoustic energy
Considering now the signals detected in a borehole in
strument, the detected signals may represent the time of 70 traversing the media forming 'the well bore from above
and below the receivers and providing at least two time
emission of an acoustic impulse and/ or represent `acoustic
energy as sensed by one or more receivers.
The detected
measurements which are averaged to provide an aver
3
3,093,811
age travel time. Means at the earth’s surface are pro
vided to accurately determine time intervals between the
emissions of acoustic impulses and arrival thereof at dif
ferent receivers from a sequence of signals developed
by the borehole instrument, the means at the earth’s sur
face providing an ultimate averaged indication based
upon acoustic energy emissions from both transmitters
and acoustic arrivals at the respective receivers.
A pair of the sequenced signals thus represents the time
interval bet-Ween the emission of an acoustic pulse and its
arrival at a given receiver. In the circuitry 14, a íirst
time interval between the emission of an acoustic pulse
and i-ts arrival at a given receiver spaced the long dis
tance lfrom the ñrst transmitter is stored in a counter
circuit. A second time interval between the next suc
ceeding acoustic emission of the first transmitter and the
The novel features of the present invention are set
arrival of acoustic energy at the receiver spaced the short
forth with particularity in the appended claims. The
distance from the first transmitter is then subtracted from
present invention, both as to its organization and manner
’the iirst time interval. The next time interval between
of operation together with further objects and advan
the emission of an acoustic impulse by the second trans
tages thereof, may best be understood by way of illustra
mitter and its arrival at a receiver spaced the long dis
tion and example of certain embodiments when taken in
tance from the transmitter is added into the counter cir
conjunction with the accompanying drawings in which: 15 cuit. The subsequent time interval between the emis
FIG. l is a view of a borehole instrument suspended
sion of an acoustic impulse by the second transmitter
in a well bore and coupled to circuitry at the earth’s sur
and its arrival at a receiver spaced the short distance from
face by a cable;
the tra-nsmitter is subtracted from the counter circuit.
FIG. 2 is a schematic representation of the circuitry
Thus, the net time interval count left in the counter is
located at the earth’s surface;
20 representative of two distinct times of travel of acoustic
FIG. 3 is a schematic representation of circuit-ry in
energy over a section of adjacent media between the two
the borehole instrument;
receivers. The net time interval Vin the counter is di
FIG. 4 is a view of typical waveforms particularly with
vided by two thereby to provide an average travel time
reference to the operation between the surface equipment
of acoustic energy over the section of adjacent media.
and borehole equipment;
25 One of the prime advantages of this system is that the
FIG. 5 is a view of typical waveforms particularly With
longer time intervals measured between an emission and
reference to the operation of the surface equipment of
detection of acoustic energy permit time for accurate
transmission lof the signals to the earth’s surface whereas
FIGS. 6a and 6b are diagrammatic views of surface
with a short spacing between receivers it is diñicult to
located time measuring means;
30 transmit the signals directly to the earth’s surface. The
FIGS. 7-9 are simplified representations of various tim
transmitters above and below -the receivers further pro
FIG. 2;
a
n
'
ing sequences of the system; and
vide for time measurements substantially independent of
FIG. l0 is a schematic representation of counter and
the instrument position relative to the wall or geometry
transfer circuits of the present invention.
of the well bore.
Referring now to FIG. 1, an acoustic Ilogging tool or 35
Reference is now made to FIGS. 2 and 3 for the respec
apparatus 10 is shown disposed in a borehole 11 by
itive details :of the surface located electrical circuitry 14
means of a cable 12. which is spooled on a reel or winch
and the electrical circuits in the apparatus 10. Also,
*13 located at the earth’s surface. The apparatus 'l0 is
reference will be made to FIGS. 4 and 5 wherein repre
preferably centered in the well bore by conventional cen
sentative waveforms for various signals in the circuit are
tering means (not shown).
40 illustrated.
The electrical circuitry in the tool 10 is coupled by the
As shown in FIG. 2, the repetitive pulsing of a trans
cable `l2 to surface located electrical circuitry 14. The
mitter in the logging instrument may be controlled by a
tool It) includes an array of transducers which may, for
periodic pulsing source `20 such as a twenty-cycle per
example, be of the magnetostrictive type and are suitably
second signal generator whichy is arranged to develop a
supported in a fixed spaced relationship to one another in 45 signal output 20a (FIG. 4a) to pulse the transmitter in
a Well-known manner in the tool.
The transducer ar
dependent of the travel oit' the tool. On the other hand,
rangement provided includes an upper transmitter T1,
the movement of the cable can be coupled by means of a
sheeve 13a in a well-known manner to a selsyn system
an upper receiver R1, a lower receiver R2 and a lower
transmitter T2 in longitudinal alignment with the spacing
between the «transmitter T1 and receiver R1 equal to the
spacing between the transmitter T2 and receiver R2. Pref
or interval timer ‘Z1 to provide pulse signal outputs to
50 the transmitter dependent upon the movement of the
cable so that the pulsing of the transmitter is keyed to
the movement of the tool through the well bore. A
switch 22 is provided to connect either of these pulsing
systems to a conventional flip-flop circuit 24 so that the
output of a pulse source causes the flip-flop circuit 24
about a plane of symmetry midway between receivers R1
to reverse its operating condition. In FIG. 4b and FIG.
and R2.
5a, a typical waveform 25a yon conductor 25 is illustrated,
The operational arrangement of the T-R-R-T system
the waveform 26a on conductor 26 being reversed in
is such that the time of emission of a pulse of acoustic
polarity and shown in dashed line.
energy from a transmitter can be reliably detected at the 60
Outputs from the ilip-ilop circuit 24 with respect tot
earth’s surface and the acoustic energy as detected by a
a ground potential are respectively conveyed by conduc~
receiver can be representatively reproduced as an elec
tors 25, 26 to flip-flop circuits 27 and 28. A conductor
trical signal at the earth’s surface and the travel time of
‘output B is provided from the output of one side of flip
acoustic energy from the transmitter and through the
adjacent media forming the well bore and back to a re 65 flop 27 and likewise, a conductor output C is provided
from the output of one side of ilip-ilop circuit 28. Con
ceiver can be measured with considerable accuracy. At
ductor loutputs B and C are coupled via cable conductors
the earth’s surface, the transmitter-to-receiver signals are
received by the circuitry 14 from the down hole tool 10l
to conductor inputs in the logging instrument (FIG. 3)
erably, this spacing is on the order of three feet and the
span between receivers R1 and R2 is ion the order of one
foot. The transmitter T1 and receiver R1 are thus sym
mertical relative to the transmitter T2 and receiver R2 55
in a sequence in which one Atransmitter is pulsed twice
which are correspondingly identiíied as B and C.
In
to provide emission signals alternating with signals re 70 FIG. 4c, the waveform 27a of the output signal on con
spectively `detected by receivers spaced a long and a short
ductor output B is illustrated while the waveform 28a
distance from the first transmitter; the other transmitter
lof the >output signal on conductor output C is illustrated
is also pulsed twice to provide emission signals alternat
in FIG. 4d. It should be appreciated that the output
ing with signals respectively detected by receivers spaced
a long and a short distance from the second transmitter.
signals on conductor outputs B and C are 90° out of
phase.
3,093,811
Referring now to FlG. 3, the conductor input C is con
nec-ted to a solenoid 32 of a receiver switch 33. Thus,
in one »operating condition of the flip-hop circuit 28, the
solenoid 32 is energized while in the other operating con
dition of the hip-flop circuit 2S, the solenoid 32 is de
energized. The solenoid actuated receiver switch 33 con
nects a common signal channel as indicated generally
by the numeral 34, to first one receiver then the other.
The conductor input B is connected to a solenoid 36 of a
transmitter switch 37. Thus, in one operating condition
of flip-flop circuit 27, the solenoid 36 is energized while
in the other operating condition of flip-flop circuit 27,
lthe solenoid 36 is de-energized. The solenoid actuated
transmitter switch 37 connects a common transmitter
channel as indicated generally by the numeral 33 to first
one transmitter and then the other.
As shown in FiG. 3, the receivers R1 and R2 are re
tial. Capacitor 60 is sized of a value in accordance with
the electrical band width of response for the cable 12 to
«transmit the frequencies in the electrical signal corre
sponding to the acoustic energy as received by a receiver
to the surface in a reliable manner. Thus, the trans
mission chanacteristics of a cable are equalized to insure
a high fidelity signal at the surface of the earth.
At the earth’s surface as shown in FIG. 2, the cable
conductor 6i from the single signal channel 34 in the
borehole apparatus 10 is connected -to an amplifier 70
which, in turn, is connected to normally closed signal
gate circuits ’71 and 72. The transmitter signal gate 71
has its gate control circuit connected to a conventional
delay circuit 73 which is, in turn, coupled by «a con
doctor 62 to the fire pulse generator 30. The fire pulse
39a (FIG. 5bk or FIG. 4e) actu‘ates the delay circuit 73
which, after a suitable time delay 73a (FIG. 5c) has
spectively connected to the poles 41, 42 of the receiver
elapsed following the development of the fire pulse 30a,
switch 33, which has its movable contact arm connected
to an amplifier ¿i7 in the single signal channel 34. Re
ceiver switch 33` as discussed above is automatically
opens the gate 7i as shown in FIG. 5d. The time delay
of circuit 73 is less `than the time delay of delay circuit
3‘9 (FIG. 3) so that gate 71 is opened prior to the arrival
of a pulse fitta indicating the triggering of a transmitter.
After gate 71 is opened yor actuated, the pulse signal 40a
operated to change positions at the time that the flip-Hop
circuit 28 reverses operating conditions.
The transmit
ters T1 and T2 are respectively connected to the poles
43, 44 of the transmitter switch 37 which has its mov
able contact arm connected to the single transmitter chan
nel 38. Transmitter switch 37 is actuated to change posi
tions at the time that the iiip- iop circuit 27 reverses oper
conveyed via the amplifier I56 of the signal channel 34,
the conductor 6l and amplifier 70 is passed through the
gate 71 to a time of occurrence of signal detector 74
which develops an output pulse 74a (FIG. 5e). The
time of occurrence detector 74 may be a suitable con
ventional triggering circuit arranged to produce an output
ating conditions.
Returning now to FlG. 2, pulse selection switch 22 is 30 trigger signal 74a (FIG. 5e) whenever the «amplitude of
an applied input signal from ampliiier '70 exceeds a pre
also coupled by a conductor 23 to a conventional delay
circuit 2.9.
Delay circuit Z9 is in turn, connected to a
“tire” pulse generator 30. The time delay of delay cir
cuit 29 is made, for example, about 9 milliseconds to en
able all of the down hole switching of switches 33 and 37
to be accomplished prior to the initiation of a fire pulse
from pulse generator âtì. Pulse generator Btl is coupled
by a conductor output A and the cable to a conductor in
put A of the transmitter channel 38 in the borehole in
strument 16 (FIG. 3). The common transmitter chan
nel 38, as shown in FIG. 3, includes a delay circuit 39
and a pulse generator 4@ which has its output coupled
to the movable arm of the transmitter switch 37. When
determined level.
Thus, the detector 7 4» is triggered upon
receipt of the signal 40a from the pulse genenator 49
while the gate 71 is open. The output signal 74a of the
detector 74 is returned to the gate 71 via a conductor 75
to close the gate 71 immediately after the ydetector ’74 is
actuated. The output signal '74a of the detector 74 is
also supplied via a conductor 76a to a iiip-tiop circuit
76 which actuates a time or count gate 77 (FIG. 5h).
Conductor 76a also is connected to a delay circuit 78
which, in response to signal 74a from the detector 74
and, after a suitable predetermined time (FIG. 5f), aotu
utes or opens the remaining gate circuit 72 for operation
(FIG. 5g). Normally, gate circuit 72 is opened by the
a fire pulse Etta (FIG. 4e) from pulse generator 30 is
transmitted through the cable to transmission channel 45 delay circuit 78 just prior to the earliest expected arrival
38 via conductor input A, the pulse 39a is conveyed to
of an «acoustic impulse at a receiver.
the »delay circuit 39. Pulse ‘39a is also conveyed via a
The timing gate 77, when turned on, permits the out
conductor 47 to a iiip-iiop circuit d5. The delay circuit
put signal (FIG. 5i) from Ia high frequency crystal os
39 has a time delay, of say, a l0() to 200 microseconds to
cillator 8€) (for example, 5 megacycles for the described
permit the receiver channel 34 to be blocked before a
T-R-R-T preferred spacing) to be supplied to a counter
transmitter is actuated, Thereafter the delay circuit 39
circuit 31 which counts the pulse output from the crystal
actuates the pulse generator 40 to develop a pulse output
oscillator. Thereafter, a receiver signal supplied via
‘40a (FIG. 4g) to «trigger a transmitter which produces
amplifier 70 »and cable conductor 61 to the receiver gate
an acoustic impulse.
72 is passed to a time of occurrence detector 82 which is
In the signal channel ‘34 (FIG. 3) the amplifier 47 is
similarly actuated upon the signal exceeding a predeter
coupled to the movable arA i of switch 33 and has its out
mined amplitude level. The output signal 82a (FIG. 5j)
put connected to a power amplifier 56. Noise gate 55 is
normally closed (FIG. 4f) for a short time duration in
of the detector 82 turns the timing gate 77 off (FIG. 5h)
and also turns the receiver gate ’72 oiï (FIG. 5g).
During the time interval that the timing gate 77 is “on”
response to the fire pulse 30a from the pulse generator
30 actuating flip-Flop 45 which controls the operation of 60 or open, a number of pulses are supplied to »the counter
gate 55. The time duration during which the noise gate
31 which number is related to the time interval between
55 is closed is made long enough to block any signal
an emitted transmitter pulse and la receiver signal. The
from the receivers for transmission to the power amplifier
55 of the signal channel 34 prior ‘to and shortly after the
actuation of a transmitter.
The pulse output 40u (FIG. 4g) which triggers a trans
counter circuit 81 is arranged to add or store the count
representing a first time interval by virtue of lan add
circuit 84 connected to conductor 25 of the iiip-ñop cir~
cuit 24. Thus, when the output signal 25a (FIG. 5a) of
mitter also is supplied from the pulse generator 4t) via a
flip-flop
circuit 24 operates nip-Hop circuit 27, the add
conductor 59 to a pulse Shaper 46 which shapes the signal
circuit 84 is simultaneously actuated (FIG. 5k) »to con
40a indicating the time `occurrence of the firing of the
transmitter. The signal Litta from pulse shaper 46 is con 70 dition the counter 81 to add or store the pulse output
from the crystal oscillator 30 during the time that timing
veyed to ampliñer 56 which is coupled via a capacitor 6i)
gate 77 is open. On the next succeeding output signal
to the central `or seventh conductor ‘o1 of cable 12. The
signal 49a from the pulse sh-aper `¿tl-6` is thus transmitted
26u (shown in dashed line in FÍG. 5a) from the Hip-flop
via the cable 12 by the mode of the seventh conductor
and the cable armor fwhich is at electrical ground poten
circuit 24, the flip-flop circuit 28 and a subtract circuit
85 are `actuated (FIG. 5l) to condition the counter S1
3,093,811
Y
8
to subtract the output pulses of the crystal oscillator 80
conductor output C of lflip-flop circuit 28. Signal 87a
from the previous retained count in the counter 81.
The arrangement operates in a sequence which may
Ifromdelay circuit 87 :actuates the transfer circuit 86
after the last time measurement and just prior to the
best be understood by a consideration of FIG. 7.
ystart of a new cycle of the system.
At the
time to, the waveforms on conductors outputs B and _C
The transfer circuit
86 when actuated immediately reads out an average net
and tlip-ilop 24 may be -assumed to be as shown in FIG.
count from the counter 81.
7 with the resulting connection of transmitter T1 to the
transmitter channel 38 and the connection of receiver R2
to the signal channel 34. Thus, as shown in FIGS. 4h
and 4k, the transmitter and receiver signals from trans
mitter T1 and receiver R2 would cause timing gate 77 to
>be open for a time interval during which the pulse output
read by the transfer circuit ‘81 is translated by conven
tional binary to analog converter (BAC) 89 into a volt
age signal supplied v»to the conventional galvanometer
9€) in a recorder (not shown) to produce an indication
representative of the net time interval measured -by .the
counter 81. Galvanometer 90 can, of course, be cali
The average net count as
of the crystal oscillator `80 is added into the counter oir
brated to indicate either time or velocity measurements’
cuit 8.1. „At the time t1 (shown in FIG. 7), flip-ilop cir
in a well-known manner.
cuit 24 actuates the subtract circuit 8S for the counter
The transfer delay circuit 87 also has its output cou
pled to a reset delay circuit 87h which, after a suitable
S11, transmitter switch 37 is unchanged and the receiver
switch 33 is actuated. Thus, transmitter T1 is connected
delay y87e (FIG. 5n), resets the counter y81 by means
to channel 318 «and receiver R1 fis connected to channel
of a reset pulse 87e (FIG. 50) a short time after the
34. The output of the crystal oscillator Si] in the time
net count in .the counter 8l bas been transferred to the
interval between lan emission of acoustic energy from the 20 transfer circuit 86 and just prior to the next tire pulse
transmitter T1 (FIG. 4h) and its arrival at the receiver
Sila so that the counter 81 is reset to measure the timing
measurements of the next lsequential operation.
R1 (FIG. 4j) is subtracted from the count in the counter
circuit 81 so that the count left in the counter 81 repre
Referring now to FIGS. 6A, 6B and FIG. l0, the
sents the time interval during which acoustic energy
`details and voverall arrangement «of the counter circuit
travelled the earth formations between the receivers R1 25 81, the subtraction circuits `R5, the addition circuits 84,
and the transfer circuit S6, will now be explained. As
and R2. At the time t2 as shown in FIG. 7, flip-flop
Shown :in FIG. 10, the counter circuit 81 is basically
circuit 24 actuates the «add circuit 84 for the counter,
comprised of a plurality of bistable multivibrator units
transmitter switch 37 is actuated ‘and receiver switch T2
81(a-k) coup-led to yone another to form a binary count
is connected to transmitter channel y38, and receiver R1
ing system. In the preferred embodiment of the inven
is connected to signal channel 34 since the receiver switch
33 remains unchanged. The output of the crystal oscil
tion, eleven such individual units' or stages are lconnected
to lone another in which the units provide a digital ou-t
lator ‘80 in 'the time interval between the emission of an
acoustic impulse from transmitter T2 (FIG. 4i) and its
'arrival at the receiver R1 (FIG. 4j) is added in the
counter and represents the time interval during which o
put representative of the number of pulses applied to
its input. For simplicity of illustration, in FIG. 6A
only the ñrst, second, and part of the last unit of the
counter 'are shown, it being understood that the inter
acoustic energy travelled between the transmitter T2 and
mediate units have similar arrangement to the system to
receiver R1. At the time t3 as shown in FIG. 7, flip-flop
be explained.
circuit 24 actuates the subtract circuit 85 for the counter,
Each multivibrator of »counter 181 has transistors 90,
transmitter switch 37 remains unchanged and receiver
switch 33 is actuated. Thus, transmitter T2 is connected et() 91 cross-coupled to one another and responsive to 4a
common input pulse to their respective bases to change
to transmitter channel 38 and receiver R2 is connected
operating positions. The input pulse signal from the
to signal channel 34. The output of the crystal oscillator
gate 77 to the first multivibrator of the counter 81 is
in the time interval between the emission of an acoustic
supplied to a common input connection 97 ‘of an input
impulse from transmitter T2 (FIG. 41') and its arrival
circuit 96 comprised of a ydi-ode 94 and capaci-tance 95
'at the receiver R2 (FIG. 4k) is subtracted from the count
in series' connection wtih each of conductors 92, 93, the
in the counter and represents the time interval during
capacitances 95 terminating in «the common input con
Iwhich acoustic energy travelled between the transmitter
nection v97 and the conductors 92, 93 being connected
T2 and receiver R2.
to the respective bases of transistors 90 and 91. Hence,
From the foregoing description it will be :appreciated
that if:
50 as the pulses of a pulse 'signal supplied via the gate
circuit 77 are applied to the respective bases of the tran
ta Áis the time of travel of acoustic energy between
sistors 9i), 91 in the ñrst multivibrator Í89, the multi
transmitter T1 and receiver R2;
vibrator reverses operating conditions for each applied
tb is the time of .travel of acoustic energy between
pulse of the pulse signal.
transmitter T1 and receiver R1;
tc is the time of travel of acoustic `energy between 55
transmitter T2 and receiver R1; and
td is the time of travel of acoustic energy between
transmitter T2 and receiver R2;
Then At, the average time of travel of acoustic energy
between receivers yR1 and R2 may be expressed as
60
Ag=ïígiïié
(1)
In the typical manner of counter circuits, in the first
multivibrator 81a, the collector of the first transistor 90
provides an output signal which indicates either :a 0 or
1 digit `and the collector Iof the :second transistor 91
provides an output signal which indicates either a 0
or 1 digit. lIn the next adjoining multivibrator ~811b and
throughout the successive multivibrator units, the lirst
transistor thereof would likewise provide an output sig
nal which indicates either a 0 cr l digit and the second
transistor thereof would provide an output signal which
The average time of travel At is thus based upon acoustic
energy emitted from above and below the receivers and 65 indicates either »a 0 lor 1 digit. To add a number of
successive pulse inputs in the binary `counter 811, the out
is an average of two distinct time measurements. This
reading minimizes errors due to tilt of the apparatus in
put of the ‘second transistor 91 of each multivibrator is
the well bore or caves in the well bore and very greatly
connected to :an input circuit 96 of the next adjacent
improves the accuracy of .the At time measurement.
multivibrator by means of output conductors 100 and
To obtain a measurement of the average net count 70 isolation resistors 100e. To subtract a number of suc
of the At time remaining in the counter 81, a transfer
cessive pulse inputs from a number of pulses which are
circuit S6 (FIG. 2) is connected to the counter 81 so
stored in the binary counter by addition, the output of
as to -divide by two the net count in the counter. The
the ñrst transistor of each multivibrator unit is connected
transfer circuit 86 is actuated by rneans of .a signal 87a
to an .input circuit 96a of the next adjacent multivibra
(FIG. 5m) from a delay circuit `87 which is coupled to 75 tor by means of output «conductors 101 4and isolation>
3,093,811
9
10
resistors ltila. Input circuits 96a are identical to input
circuits 96 and are connected in parallel.
To perform the yaddition of separate and distinct pulse
delay circuit 87 (after the net count is in counter 81) is
supplied to input 113 which causes the transistors in the
transfer switches 111, 112 of each multivibrator unit
110(b-k) to conduct in preference to the conductive state
inputs, add circuits S4 are connected to the subtract out
put conductors itil. The add circuits £54 are provided Cil of the corresponding transistor 9i) or 91 in the counter
81 so that the respective transistors 96a and 91a in each
with add switches 103 in the form of ltransistors which,
when actuated by a `commonly applied pulse signal, short
multivibrator unit INQ7-k) align their respective con
the subtract output conductors 161 to ground so that
only the add outputs of second transistors 91 on conduc
tors 10u are effective in operating the muitivibrators.
To perform the subtraction of a pulse input, subtract cir
cuits 85 are connected to the add >output conductors 100
to adjacent multivibrator-s. The subtract circuits 85 are
ductive states to` correspond to the respective conductive
states of transistors 90 and 91 in the counter S1. Thus,
the net count in the last ten units of counter S1 is trans
ferred to the multivibrator units 110 of the transfer cir
cuit 86. An output conductor 118 coupled to the sec
ond transistor of each of the multivibrator units 110(b-k)
and connected to the BAC circuit 89 which converts the
likewise provided with subtract switches 164 in the form
of transistors which, when actuated by a commonly ap 15 digital number of the multivibrator units 11tl(b-k) into
an `analog voltage signal in a welhknown manner.
plied pulse signal, will short the add output conductors
It should be appreciated that the number of multivi
100 to ground so that only the subtract outputs on con
brator units of counter S1 may be less than the number
ductors lill are effective in operating the multivibrator
required to count the entirety of pulses from an add in
units. Thus, it will be appreciated that the add switch
circuits 84, when actuated by a `common signal from the 20 put provided that the number of units are adequate to in
d-icate the difference between an add and subtract inputs.
It should also be appreciated that the described timed
sequence of signals between the transmitter and receivers
flip-»flop circuit 2li, cause, the counter `S1 to add the pulse
output from the crystal `oscillator during the time gate
'77 is open. The time that gate 77 is open is determined
by the time of pulsing ‘of a transmitter and the subse
quent arrival of the acoustic energy at a »far receiver for
example, between transmitter T1 and receiver R2. When
the flip-Hop circuit 24 reverses its operating conditions,
ÍS T1R2-T1R1+T2R1--T2R2This sequence may, for example, be changed by re
versing the output connections B and C to the input con
nections B and C of the borehole instrument 10. Assum
the subtract switch circuits 8S are actuated and the count
er 81 is then conditioned to subtract the pulse output from
ing that B’ (not shown) is the output of iiip-iiop 27
time ‘of pulsing `of a transmitter and the subsequent ar
rival of the acoustic energy at a near receiver, for exam
ment 10; then as shown in FIG. 9, the counter S1 would
connected to input connector C in the instrument 10 and
the crystal oscillator during the time gate 7‘7 is open. 30 that C' (not shown) is the output of the second stage
flip-flop 28 connected to input connector B in the instru
The time that gate ‘77 is `open is now determined by the
ample, transmitter T1 and receiver R1. The net count 35
of pulses are digitally stored in the counter circuit 81
measure a sequence as follows:
`after addition and subtraction represents the net time
for acoustic energy to travel the earth formations be
tween the two receivers. Thus, the next addition and
In the case of FIG. 8, the net count remaining in the
counter 81 even though .represented by a negative num
ber is still representative of the travel time.
leave a net count in the counter of two net times for
connector C in the instrument 10 by a conductor B” (not
Vacoustic energy to travel the earth formations between
two receivers where the net times are derived from puls
ing of a transmitter above and below the detecting re
ceivers.
The average net count in the counter circuit $1 is read
Eout in the following manner. A transfer circuit 36 is
the counter `81 would measure a sequence as follows:
In still another example, of the first stage `of flip-flop
subtraction of pulses representing the travel time of 40
27 rather than the second stage Iis connected to input
acoustic energy between Tl--Rg and "T2-_R2 respectively
shown) and a conductor C’ (not shown) is the output of
the second stage `of flip-flop 2S connected to input con
nector B in the instrument 10; then, as shown in FIG. l0,
T2R1- TiRi-l- TiRz- TzRz
In this case the net count remaining in the counter
provided which is comprised of multivibrator units
would still be representative of the travel time.
11ti‘(b~k) identical to the multivibrator units Z9 of the
Other sequences are `also possible provided that the
50
counter circuit 81 except that a multivibrator unit corre
main objective of subtracting the lesser time measure
sponding to the multivibrator unit 81a of counter -81 is
omitted. Thus, ten multivibrator units llMb-k) are
provided. The ten such multivibrator units »1MM-k)
are connected to the last ten units 8Mb-k) of the counter 55
plished. This is made possible because only the net count
fer switch 111 and 112 in the `form of a transistor. The
transistors of the switches 111 and 112 have their collec
tors connected to the respective collectors of the multi
be used to divide the total count in the counter 81 by a
factor of two.
ments Ifrom the greater time measurements is accom
in the counter is read out.
Thus, the sequence of enter
ing the time measurements may be changed without af
fectíng the net count provided that the addition and sub~
is effectively divided by a factor o-f two thereby provid
traction is properly related to obtain the average time At.
ing an average net count in the transfer circuit `36.
t will also be appreciated that while the average net
In the transfer circuit S6 as shown in FIG. 6B, each
count is obtained by dividing the count in counter 81
of the multivibrator units has transistors 99a and 91a. 60 by a particular relationship between the counter S1 and
Transistors 90a and 91a are each provided with a trans
transfer circuit S6, other Well-known arrangements may
81 so that a transfer l.of the net count in the counter 81
While particular embodiments of the present invention
vibrator transistor 96a and 91a and the respective emit 65 have been shown and described, it is apparent that
ters of the transistors in switches 111 and 112 are con
changes and m-odiñcations may be made without de
nected to a common input 113. Input 113 is common
parting from this invention in its broader aspects and,
to all of the multivibrators 11tl(b-k) and has input ter
therefore, the aim in the appended claims is to cover all
minals 113@ and 113k where terminal 113a is connected
such changes and modifications as fall within the true
to switches 111, 112 and terminal 11319 is connected by 70 spirit and scope of this invention.
What is claimed is:
a resistance `115 to ground. The bases of the transistors
l. An acoustic logging system for use in a Well bore
in the respective transfer switches 111, 112 are respec
comprising: a borehole instrument sized for passage
tively coupled by conductors 1&5, 106 to the outputs of
through a well bore and having spaced upper and lower
a corresponding positioned multivibrator in the counter
81. In operation, an input or transfer signal 87a from 75 acoustic transmitter means and at least two acoustic re
3,093,811
l2
ceiver means therebetween, means coupled to said trans
mitter and receiver means for developing signals repre
senting transmitter-to-receiver acoustic travel times for
successive depth intervals between each of said trans
transfer means coupled to said counter means and re
sponsive to a transfer signal to read out a net pulse count
in said counter means, means to key said counter means
and transfer means in sequence to .obtain an addition and
mitter means and each of said receiver means; means
subtraction of at least two pulse signals representing time
coupled to said signal developing means to provide coun
interval signals for a given depth in a well bore and
provide a transfer signal to said transfer means to transfer
ter pulse signals in response to said developed signals,
counter means coupled to said counter pulse signal means
for adding and subtracting at least two pulse signals from
such net pulse count in said counter means to said trans
fer means, and means coupled to said transfer means to
said counter pulse means representing at least two trans 10 derive indications of the net pulse count in the counter
mitter-to-receiver acoustic travel times for a given depth
at the time of occurrence of a transfer signal.
in a well bore to provide a net pulse count, transfer means
coupled to said counter means and responsive to a trans
fer signal to read out a net pulse count in said counter
means, means to key said counter means, said transfer
means and said signal developing means in sequence to
obtain an addition and „subtraction of at least two pulse
4. In an acoustic logging system for use in a well bore
wherein it is desired to measure the difference between
signals representing transmitter-to«receiver acoustic travel
coupled to said counter pulse signal means for adding and
subtracting at least two pulse signals from said counter
pulse means representing at least two time interval signals
times for a given depth in a well fbore and provide a trans
fer signal Ito said transfer means to transfer 4such net pulse
count in said counter means to said transfer means, and
means coupled to said transfer means to derive indica~
at least two independently derived time Ainterval signals
which are derived for successive depth intervals along a
well bore, means to provide counter pulse signals in re
sponse to time interval signals, digital counter means
for a given depth in a well bore to provide a net pulse
count, digital transfer means coupled to said counter
.tions of the net pulse count in the counter at the time of
means and responsive to a transfer signal to read out a
occurrence of a transfer signal.
net pulse count in said counter means, means to key said
2. An acoustic logging system comprising: a borehole
instrument sized for passage through a well bore and
having an upper and lower acoustic transmitter means,
counter means and transfer means in sequence to obtain
an addition and subtraction of at least two pulse signals
representing time interval signals for a given depth in a
well bore and provide a transfer signal to said transfer
and upper and lower receiver means therebetween, signal
channel means in said instrument, transmitter actuating
means to transfer such net pulse count in said counter
means in said instrument including an output to said 30 means to said transfer means, and means coupled to said
signal channel means, receiver switch means coupled be
transfer means to derive indications of the net pulse
tween said receiver means and said signal channel means
count in the counter at the time of occurrence of a
for selectively connecting one or the other of said receiver
means to said signal channel means, transmitter switch
means coupled between said transmitter means and said
transmitter actuating means for selectively connecting one
‘5. In an acoustic logging system for use in a well bore
wherein it is desired to measure the difference between at
or the other of said transmitter means to said transmitter
:least =two independently derived time interval signals for
transfer signal including a digital-to-analog converter
means and recorder means.
actuating means; surface located means coupled to said
successive depths along a well bore, a gate circuit opera
switch means and said transmitter actuating means for
tive in response to time interval signals for passing pulse
keying the operation of said switch means and said trans 40 signals therethrough during the time interval of such time
mitter actuating means in a repetitive sequence to con
interval signals, a idigital counter circuit coupled to the
nect one of said transmitter means to said transmitter
output of said gate circuit and a clock oscillator to pro
actuating means once for each connection of the respec
vide pulse signals coupled to the input of said gate cir
tive receiver means to the signal channel means and the
cuit, said counter circuit including add means to condi
other of said transmitter means to said transmitter actuat 45 tion said counter circuit to add a pulse signal from said
ing means once for each connection of the respective re
clock oscillator during one time interval when said gate
ceiver means to the signal channel means, means cou~
is operative and subtract means to condition said counter
pled to said signal channel means to provide counter
circuit to subtract a pulse signal »from said clock oscillator
pulse signals in response to signals representing trans
during another time interval when said gate is operative
mitter-to-receiver acoustic travel time, counter means cou 50 thereby to provide a net pulse count in said counter
pled to said counter pulse signal means for adding and
subtracting pulse signals from said counter pulse means
to provide a net pulse count, transfer means coupled to
said counter means and responsive to a transfer signal to
means, digital transfer circuit means coupled to said
counter means and responsive to a transfer signal to read
out a net count of pulse signals in said counter circuit
representing the «difference between added and subtracted
read out a net pulse count in said counter means, means 55 pulse signals in said counter, means to key the operation
coupled to said keying means to actuate said counter
of said add, subtract and transfer circuit means in a se
means and transfer means in sequence to obtain an
'lected sequence to obtain an addition and subtraction of
addition and subtraction of at least two pulse signals
pulse signals, and a transfer of a net pulse count, circuit
representing transmitter-to-receiver travel times for a
means coupled to said transfer circuit means for convert
given depth in a well bore and provide a transfer signal 60 ing a net pulse count in said transfer circuit means into
to said transfer means to transfer such net pulse count
an analog signal, and means coupled to said converting
in said counter means to said transfer means, and means
circuit means for indicating the time difference between
coupled to said transfer means to derive indications of
added and substracted time intervals as represented by
the net pulse count in the counter at the time of occur
such analog signal for successive depth intervals in a well
ence of a transfer signal.
65 bore.
3. In an acoustic logging system for use in a well bore
6. An acoustic logging system for use in a well bore
wherein it is desired to measure the difference between
comprising: a borehole instrument sized for passage
at least two independently derived time interval signals
through a Iwell bore and having spaced upper and lower
which are derived for successive depth intervals along a
acoustic transmitter means and at least two acoustic re
well bore, means to provide counter pulse signals in 70 ceiver means therebetween, means coupled to said trans
response to time interval signals, counter means coupled
mitter and receiver means `for developing signals repre
to said counter pulse signal means for adding and sub
senting transmitter-to-receiver,acoustic travel times for
tracting at least two pulse signals from said counter pulse
successive depth intervals between each of said trans
means representing «at least two time interval signals for
mitter means and each of said receiver means; means
a given depth in a well bore to provide a net pulse count, 75 coupled to said signal developing means to provide
3,093,811
13
counter pulse signals in response to said Vdeveloped signals,
14
coupled «to said counter digital counting units beginning
for adding and subtracting at least two pulse signals from
with the second of said counter digital counting units
thereby to divide the net count in said counter means by
said counter pulse means representing at least two trans
a factor of two.
counter means coupled to said counter pulse signal means
mitter-to-receiver acoustic travel times for a given depth
in a well bore to provide a net pulse count, said counter
means being comprised of digital counting units, transfer
means coupled to said counter means and responsive to a
7. The apparatus of claim 6 wherein the number of
said counter ydigital counting units is great enough to
count the net difference between at least two pulse signals
from said counter pulse means but less than the number
of counter digital counting units «required to count the
transfer signal to «read out a net pulse count in said counter 10 greatest pulse signal from said counter pulse means.
means, said transfer means being comprised of digital
No references cited.
counting units, said transfer ldigital counting units being